NVA AP50 INTEGRATED AMPLIFIER

The AP50 forms the third in the range of integrated amplifier.

Specifications

Inputs Six line level

Outputs 4mm speaker sockets.Tape out.

Power supply 1 x 160 VA

Power Output 50 W

Dimensions 430mm x 90mm x 320mm (whd)

AP50 Integrated Amplifier

An internal phono stage is available for this amplifier. For turntable use you must use that or an external phono stage like the NVA Phono 1, Phono 2 or equivalent. All 6 inputs are identical and hardwired to the selector switch using silver alloy cable with PTFE cover. The output of the switch is routed to the potentiometer and tape socket again with the silver alloy cable. The potentiometer is a very high quality. The signal is then routed to the amplifier PCB again with silver alloy cable. The pre-amp stage is entirely passive. The input to the power amp stage has minimum capacitive and inductive coupling and has been designed to operate correctly with the variable impedance output of a passive pre-amp stage. A current mirror operates at the pre-driver stage to ensure that the voltage rails track each other correctly. The driver stage has both current and voltage amplification using devices that could be used as output transistors. The output devices are 12 amp darlingtons and there are two per channel.

The power supply is based around one 160va transformer. A two way smoothing stage is incorporated in the supply. There is no protection circuitry or filtering on the output of this amplifier so care must taken in its usage.

Do not short circuit the output. Do not use bi or tri wire (unless nva LS1, LS3 or LS5) or high capacitance or litz type loudspeaker cables as these will damage the amplifier as they create a virtual short circuit at very high frequencies which will create instability in the amplifier. As a rule of thumb avoid cables with a capacitance higher than 200pF per meter. Simple solid core or low capacitance stranded cables are cost effective but high quality silver or silver alloy cables such as NVA LS1 or LS3 are best. Avoid loudspeakers with an average of below 4 ohms load impedance or loudspeakers using high frequency notch filters in their crossovers. This amplifier has minimum capacitors, no inductors, and is a low negative feedback class AB circuit design that is unique. The amplifier has an output of 50W per channel. The case design has been created for sonic reasons and is glued and insulated to stop induced circulating currents and static charge problems associated with normal case designs. Due to the power supply nature of the design of this amplifier do not expect it to reach the design sonic performance until used for at least one week from new. It is recommended that the amplifier is left on at all times. Loudspeaker cables can be disconnected but do this at the amplifier end to avoid short circuits.

Hi-Fi News Review

MINIMAL ART

The NVA AP50 integrated amp is a return to British solid state minimalism

After it's burned in for a few weeks, the AP50 reveals surprising qualities like smoothness to rival vintage valve confectionery

How refreshing it is to see, amidst a plethora of amps so cluttered as to be rococo, a return to good old-fashioned British minimalism. Not that NVA is completely innocent of the charge of producing what in the world of watches are called 'complications'; the company's flagship models are as ornate, stylised and over engineered as any Japanese single-ended triode amplifier or computer-driven solid-state behemoth from America. But NVA's AP50 integrated amplifier is a dose of sanity as the hi-fi buttons 'n' knobs count increases with the number of surround-sound formats on offer.

This amp is so cleanly styled that it'll confuse those introduced to audio through an A/V receiver of post-1990 construction. Then again, it's not surprising, as Richard Dunn is the industry's self-appointed pomposity filter, author of numerous missives protesting one thing and another. But he does practice what he preaches, and the AP50 is as free of taurean faeces as is possible without eliminating basic operations. Even the on-off toggle has been relegated to the back panel, which houses only the requisite (gold-platted) sockets for the six sources, the tape loop ingress and egress, and speaker sockets which accept only the near-to-extinction banana plug. The front panel bears but two large knobs, one a nicely weighted device for altering level, the other for selecting the source. As the front NVA panel is made from black perspex, NVA has used this to good effect by including a tiny red LED to indicate on/off status in a most tasteful manner. But it won't cause palpitations among those who get their rocks off by switching off the lights to watch their hi-fi systems luminous capabilities. All we're talking about is a tiny red dot.

Er, that's it. The unit is so clean and simple and nicely finished that, were the dealer to cover the NVA logo, you could easily mistake it for a Densen integrated amp or some other device of the Scandinavian persuasion. The amplifier is a tonic for those fed up with clutter, a throwback to 1983 and the days when anyone using a source other than a turntable was deemed an untermensch. : phono is optional.

TECHNOLOGY

In the form which arrived for the review, the AP50 bore six identical line inputs, hardwired to the selector switch. NVA - as cable-sensitive a company as I've ever faced - uses silver alloy with a PTFE cover at this stage. The output of the source switch is fed to the volume control and tape sockets, again via silver wire. The potentiometer is an ultra high quality 'cermet' type using precision metal film resistors 'as a bypass to simulate a log law'. The signal is fed to the amplifier PCB again through hard-wired silver cabling.

CABLE MANNERS

There's a list of acceptable wires which accompanies the AP50 naming seven precise makes and models of wire at the top of the tree (two from NVA, all types of DNM), and a roster of 22 others which pass muster. And just in case you think that Dunn is kidding, the sheet also states categorically that, 'If any other cable than the recommended are used it will invalidate our guarantee'. And should you entertain the notion that such a stipulation is illegal, I think you'll find that the warning qualifies as valid instructions for use, and to ignore it would be like expecting a car manufacturer to pay for a new catalytic converter when you've been using leaded petrol.

Although I'm loath to cite a revival in passive pre-amplification, despite this technology rearing its head in all manner of unlikely places, the front-end of the AP50 is completely passive, with Dunn pointing out that there's a wee trade-off in using the cermet pot. Apparently, the cermet tracks are not as smoothly finished as conductive plastic film or carbon tracks, so there's a form of 'surface noise' just audible when you alter the volume. But Dunn argues that cermet provides far better sound quality than alternatives, so the residual noise during level changes is a small price to pay for sonic superiority. And besides, you do your listening when the levels are set and the rotation has stopped. (No, let me guess: There's a rare breed of Tasmanian audiophiles who listens to music with the volume constantly changing...)

Because it's fed by a passive pre-amp, the input stage of the power amplifier section has minimum inductance and capacitance, and a current mirror is employed to guarantee that the volume rails track each other correctly. Overkill has been applied in the power amps driver stage in that both the current and voltage amplifiers use devices hefty enough to act as output transistors; the actual output devices are 12 amp Darlingtons, two per channel and responsible for its 60W/ch rating.

NVA also eschews in this product any form of protection circuitry, which should be kept in mind when you first read the detailed instructions and warnings of locusts and boils should you behave in an unnatural manner. Grounds for turning you into a pillar of salt include short circuits, bi- or tri-wiring, running greater than 10 meters, using 'unapproved cables', high capacitance or Litz wires, or listening to Babylon Zoo CDs. Indeed, so fearful was I of incurring the wrath of Dunn that I didn't stray from using the supplied NVA cable. Again in the interests of sound rather than 'unconditional stability', the AP50 employs the minimum number of capacitors, no inductors, low negative feedback, and Class AB operation. A 160VA toroidal transformer with a 25 amp bridge rectifier and a unique filtering system for the power supply. Even the case is slightly odd in the interests of sonic excellence; it's non-magnetic, glued together, and insulated to prevent static charge problems, and to stop induced circulating currents. Hell, Dunn has filled a 12-page 'white paper' with NVA philosophy, an audio Mein Kampf which makes fascinating reading if you don't mind being beaten over the head with an audio designer's beliefs. Fortunately for Dunn, he tends to make sense. Which is why the AP50 is such as killer

To everyone's dismay, there are dozens of amps out there for circa £520 which do wonderful things. Expand the sector to embrace £450-£700 and you find all sorts of goodies, including the delicious Densen Beat, some entry-level tubeware, British perennials, the better Japanese integrateds and limitless second-hand opportunities. Clear winners that obviate the existence of all others? That's wishful thinking on the part of magazines which gives awards for 'Best In Its Class'. Such a beast cannot exist because there's no such thing as a universal solution. Which is why cranky hardware like the AP50 actually has an easier time in the market than any of the half-dozen top-rated Asian 50-watters which compete for the exact same customer.

Dunn's logic is as transparent as the amplifiers sound: if you lay down a specific set of rules, you've (1) focused on the customers prepared to meet those criteria and avoided the time-wasters and the 'ineligibles', and (2) ensured that the amplifier will be used correctly. Admittedly, such an approach in anathema in business terms: it's the deliberate limiting of a product's appeal. But it doesn't half make life easier all round. And your customers will know exactly what they're getting.

SOUND QUALITY

If a gun were held to my head and I was forced to cite but one trait which defines the sound of the AP50, I'd have to say it's the overall silkiness In the case of the AP50, it's an amplifier that - without drama - gets on with the job. It drove a weird mix of speakers (despite my ignoring the command to avoid speakers which might possess 'high frequency notch filters'), including the original Quad ESL, Sonus Faber Concertinos, LS3/5As, Boleros, and the Rega headphone adapter, and never less than satisfactorily. The unit never showed signs of distress. Asked to play loudly, it rocked. Asked to play softly, it did so with the dynamics intact. But it had a few secrets which it didn't yield so readily, and I was misled into thinking that the AP50 was simply a minimalist alternative to the Rotels, Pioneers and NADs of the world, or yet another Britamp to place alongside Arcams, Naims or Audiolabs. Big mistake. After it's burned in for a few weeks, the AP50 reveals surprising qualities like smoothness to rival vintage valve confectionery. Although it's most evident in the region normally plagued by digital coarseness, this refinement also blessed all manner of vocals with a resistance to the shame of sibilance. If a gun were held to my head and I was forced to cite but one trait which defined the sound of the AP50, I'd have to say it's this overall silkiness. Which is not something I'd expect of a mid-priced, solid-state integrated amplifier.

Whatever Dunn's current feelings about soundstage and imaging, the AP50 is almost Yank-like in its three dimensionality. It's about as far from the 2D sound favoured by UK flat-earth amp builders as is possible for such sane money, and this begs the use of precise performers (in the imaging stakes, that is) like small two-way systems of the LS3/5A calibre. Perhaps there was some sort of mismatch with the Quads, but imaging was the one area which wasn't exploited when the AP50 faced the legendary electrostatic.

Sticking with the kind of two-ways likely to be used with an affordable solid-state integrated, I was overjoyed to learn that the AP50 avoided, like the plague, the kind of heightened hygiene, that aggravating sterility which too wham-bam-thank-you-ma'am sessions suggest is true transparency. The AP50 strips away nothing, and I implore you to audition it with rich vocals if you want to learn just what it can do. Arm yourself with some Nat King Cole, Keb' Mo', Johnny Rivers, or Howard Tate to hear the most detailed textures, and Nanci Griffith or Joan Baez to hear unbridled clarity without glassiness. And that's one hell of an accomplishment at the price.

WE ARE SO CONFIDENT IN THE QUALITY OF OUR PRODUCTS AND DESIGNS WE OFFER 30 DAY NO QUIBBLE RETURNS POLICY

Available in 120v or 240v please stipulate on purchase

NVA's Overall Philosophy

Generally, we have never been keen on producing conventional literature, because it's usually just glossy expensive paper full of pretty meaningless specifications which have little bearing on how good the sound of audio equipment is when playing music. If you buy hi-fi equipment on the basis of what a manufacturer says about himself (including us!) you really do deserve what you get.

As an alternative, one of our dealers suggested that we try to explain good design and how to recognize it. People probably won't believe this, but really the basics are very straightforward. A famous British amplifier designer is supposed to have said, "Good amplifier design is not the things that you do right, but the things you don't do wrong". I really wish I had said it first, because it's amplifier design in a nutshell. You can come up with all the new circuit configurations under the sun such as feed forward, low feedback, class A to Z, but ignore the common sense ground rules, and you will have a sonic bag-of-nails capable of being blown away by a couple of EL34's in a 1950 Williamson tube circuit. I am afraid 80% of the amplifiers built today fall into this category. The thing that never stops amazing me is that so many audiophiles keep falling for it. There is nothing like a good story to have people hocking the next three years' spare income on the latest all-singing, all-dancing creation. Not only that, a good story sells magazines as well, which just exacerbates the problem.

Here are my ground rules:

1. There is only one thing better than the best component money can buy, and that is no component at all.

2. Never use two components when you can do the job with one.

3. Screw up your earth (ground) paths at your peril.

4. Always use the largest transformer (toroid if possible) you can cost in.

5. If your ears and your test equipment tell you two different things, trust your ears.

6. If you have a fault in your source material or elsewhere in the equipment chain, you cannot correct it by creating an inverse fault in the amplifier with tone, balance, and filter controls. Two wrongs do not make a right.

After that it is all down to experience, and fine-tuning the design to your own taste. It is easier to get a half-way decent sounding amp using Vacuum State Logic (warm glass bottles) than Solid State Logic (hopefully cool lumps of plastic) because there is less to do wrong (Neanderthal Logic). That is why so many people have jumped on the valve bandwagon. All things being equal, bits of doped silicon encapsulated in metal or plastic (transistors) potentially are capable of doing more things with music, i.e. wider (frequency), larger (amplitude), cleaner (distortion and noise) for less cost. Remember though, the more you try to do, the exponentially easier it is to do it wrong.

If you can get most of it right, then think very carefully before you try to get the very last bit, because you may be too clever and ruin everything you've gained thus far.

This explanation is all very simplistic of course, and common sense and experience must apply as well. For example, a Class A circuit is a lot simpler that the equivalent Class B or AB. Ergo, applying my logic it should be better. Wrong, unless you spend a fortune on the power supply, which then makes the amplifier grotesquely expensive and heavy. The problems of current demand by the amplifier outweigh the simplicity. If I could buy 1000VA transformers not larger than 4" square, and weighing less than two pounds for £10, and if I could get good and consistent output transistors (i.e. not FETs) that could sink 20 amps, and either, not get hotter than 70 degrees C doing so, or stand 150 degrees C without going into self-destruct mode, I would produce Class A amplifiers. I will not produce them just because they have become some reviewers latest buzz word.

Every amplifier has its own sonic character, which is very much down to the musical parameters that are most important to the designer. The process is very much "lose on the swings, gain on the roundabouts". I once knew an amplifier designer, in fact I employed him back in Tresham Audio days to produce a professional FET power amplifier, who saw no necessity for listening to the amplifier at all. It was only after he left, and some ears were applied to the design that it started to sing, not as much as the best hi-fi amplifiers, but it went very loud and was virtually indestructible.

My greatest hang-up is information retrieval - musical information, especially dynamic separation. I will always go for information even at the expense of upsetting the "make everything bounce and swing with the tempo" brigade. My other priority, which seems to be out of favour at the moment, is neutrality, or as I prefer to call it, lack of the irritation factor.

Richard Dunn, Founder and Owner, NVA

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PLEASE NOTE ALL NVA PRODUCT IS BUILT TO ORDER SO THERE WILL BE A DELIVERY DELAY AS THE PRODUCTION AND TESTING IS SCHEDULED. AVERAGE DELIVERY TIME IS FIVE TO SEVEN DAYS BUT CAN ON OCCASION GO OUT TO FOURTEEN DAYS DEPENDING UPON ORDER PRESSURE

We offer a 100% trade in value on our products if you trade up within the nva range of like products within two years of your purchase date (only applicable to direct sales from us or through ebay). After that date we will still trade in your item but on a sliding scale as to age and condition. You must print out and keep your ebay receipt or invoice to verify your purchase date.

THIS SERVICE AND OFFER IS QUITE UNIQUE IN THE WORLD OF AUDIO AND HI-FI

NVA AND SPEAKER CABLE SAFETY

For best sound the amplifier should be left powered up. Electricity consumption is very low. It is for this reason that the power switch is located on the back panel, where it may not be easy to reach. Turn the amplifier off when you do not intend to listen to it for extended periods.

NVA amplifiers are unique, and one thing that makes them so is the minimal compensation for the output stage. It is very possible to send this amplifier into oscillation by connecting too large a capacitive load on the output, the usual culprit being unsuitable speaker cable such as Litz or Goertz type constructions. The amplifier normally runs cool, but if it is driven unstable the output transistors will become hot and the sound will distort and the amplifier could fail putting your loudspeaker coils in danger. You can check for this by placing your hand on the amplifier and feeling for hot spots. If you find the amplifier overheating switch off immediately and consider changing your cable.

Only NVA LS1, LS2, LS3, LS5 is recommended for use with this amplifier, other cables invalidate our guarantee. If you insist on using other cable please ensure it is no more than 200pf per metre and it should not be used in lengths over 10 metres. If you wish to Bi-Wire this can only be done with NVA cable and they can be made that way on order for small added cost.

For design performance only NVA Soundpipe Super Soundpipe or Soundcord  Interconnects should be used, but this is for sonic as opposed to safety reasons.